The key difference between utricle and saccule is that utricle is most sensitive when the head tilts in the horizontal plane while saccule is most sensitive when the head tilts in the vertical plane.
The vertebrate inner ear consists of different parts. The utricle and saccule are two otolith organs in the vestibular system of the inner ear. In fact, they are saclike structures. They are essential in perceiving linear acceleration (with respect to gravity) both horizontally and vertically. They possess a sensory epithelium that consists of hair cells and associated supporting cells to perceive information regarding the head movement. Utricle detects the linear accelerations in the horizontal plane while saccule detects the linear acceleration in the vertical plane. Therefore, they lie at 90 degrees to each other. Any position of the head can be detected by these otolith organs of the inner ear. They are located between the semicircular ducts and the cochlea.
CONTENTS
1. Overview and Key Difference
2. What is Utricle
3. What is Saccule
4. Similarities Between Utricle and Saccule
5. Side by Side Comparison – Utricle vs Saccule in Tabular Form
6. Summary
What is Utricle?
Utricle is one of the two otolith organs in the vestibular system of the inner year. It is the dominant organ out of the two otolith organs. It contains a sensory epithelium composed of hair cells and associated supporting cells. Therefore, it is a sensory organ. It is most sensitive in the detection of linear acceleration and the tilting of the head in the horizontal plane.
Figure 01: Utricle
Furthermore, it is larger than the saccule and is located at the top of the bony labyrinth. Utricle is also important in the reflex control of the muscles of the legs, trunk, and neck, which keep the body in an upright position.
What is Saccule?
Saccule is the small otolith organ in the vestibule of the inner ear. It is a part of the balancing system (membranous labyrinth) in the vestibule. Similar to the utricle, it is a sensory organ containing the specialized epithelium called the macula.
Figure 02: The Inner Ear
It is more sensitive when the head tilts in the vertical plane. When the head moves vertically, it translates head movements into neural impulses for the brain to interpret.
What are the Similarities Between Utricle and Saccule?
- Utricle and saccule are the two otolith organs in the vertebrate inner ear.
- In fact, they are sensory organs.
- They lie at 90 degrees to each other.
- Utricle communicates with the saccule through the utriculosaccular duct.
- They are part of the balancing system in the vestibule of the bony labyrinth.
- Both organs provide information about linear acceleration.
- They have a sensory epithelium containing hair cells and associated supporting cells.
- They use small stones and a viscous fluid to stimulate hair cells in order to detect motion and orientation.
What is the Difference Between Utricle and Saccule?
Utricle is an otolith organ of the vestibular system that detects linear acceleration and when the head tilts in the horizontal plane. Saccule is the otolith organ that is sensitive when the head tilts in the vertical plane. So, this is the key difference between utricle and saccule. Furthermore, the utricle is larger than the saccule. Therefore, we can consider this as the structural difference between utricle and saccule.
Moreover, utricle is situated at the top while saccule is situated at the bottom of the labyrinth. When considering their macula, the macula of the utricle is present on the floor of the utricle while the macula of saccule is present in its medial wall. Thus, this is another important difference between utricle and saccule.
Summary – Utricle vs Saccule
Utricle and saccule are two sensory organs and two otolith organs in the inner ear of the vertebrates and are responsible for the maintenance of static equilibrium. They contain specialized epithelia containing an array of hair cells. Among the two organs, utricle appears to be the dominant structure. It is larger than the saccule too. Utricle is more sensitive when the head tilts in the horizontal plane. In contrast, saccule is more sensitive when the head tilts in the vertical plane. Thus, this is the key difference between utricle and saccule.
Reference:
1. Purves, Dale. “The Otolith Organs: The Utricle and Sacculus.” Neuroscience. 2nd Edition., U.S. National Library of Medicine, 1 Jan. 1970, Available here.
2. Hawkins, Joseph E. “The Physiology of Balance: Vestibular Function.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 25 Oct. 2018, Available here.
Image Courtesy:
1. “Figure 36 04 04” By CNX OpenStax –(CC BY 4.0) via Commons Wikimedia
2. “Blausen 0329 EarAnatomy InternalEar” By Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014”. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. – Own work (CC BY 3.0) via Commons Wikimedia